Detecting vorticity, defined as \((\mathbf {r}, t)= \nabla \times {\mathbf {v}}(\mathbf {r}, t)\) ,[1]}
is not a trivial task, since it is singular on the vortex lines and zero outside them (a Dirac delta function).[2]}
A more convenient way to identify regions of potentially non-zero vorticity in the superfluid
is to calculate the curl of the atom current density,
\(_{ps}(\mathbf {r}, t)= \nabla \times {\mathbf {j}}(\mathbf {r}, t)\) , called pseudo-vorticity.[3]}
Plots of the iso-surfaces \(\Vert _{ps}(\mathbf {r}, t)\Vert = C\) 
allow to visualize regions of non-zero pseudo-vorticity,[4]} that may be subsequently analyzed seeking for
vorticity inside them.
